1. Field of the Invention
The present invention relates to an image transmission apparatus and an image transmitting method for transmitting image data via a network using wired or wireless technologies.
2. Description of the Related Art
A conventional image transmission apparatus periodically captures a displayed image, and transmits the captured image data from the displayed image to an image reception apparatus. However, even when no changes or merely local changes occur in the image, the entire image, including unchanged portions, is processed, thus causing wasteful processing. To solve this problem, a method has been contemplated to extract changing pixels using coordinate information in the image and the like and process only those extracted changed pixels.
However, the above-mentioned processing cannot be performed if there is no means for finding locally changing areas in the image using coordinate information and the like. Therefore, JP-A-2004-242152 discloses an alternative method which periodically captures an entire image to compare current image data captured from the image with the last transmitted image data, and transmits the image data to an image reception apparatus only when differences are found therebetween.
However, the method disclosed in the above patent document periodically captures the entirety of a current image even when there is no change from the last transmitted image. Generally, the time required for capturing an image written in a video memory is significantly longer than the time required for writing an image into the video image. Therefore, it is not an appropriate method to capture an entire image for purposes of detecting changes in the image. Also, the capturing an entire image even when there is no change in the image puts a large wasteful load on the CPU (Central Processing Unit), which controls the image transmission apparatus. This causes a problem of preventing the CPU from operating other application software.